From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from metis.ext.pengutronix.de ([2001:6f8:1178:4:290:27ff:fe1d:cc33]) by merlin.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1V7iPC-0006Y8-94 for barebox@lists.infradead.org; Fri, 09 Aug 2013 08:50:43 +0000 Date: Fri, 9 Aug 2013 10:50:19 +0200 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Message-ID: <20130809085019.GT6104@pengutronix.de> References: <20130809073237.GA26614@pengutronix.de> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20130809073237.GA26614@pengutronix.de> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Sender: "barebox" Errors-To: barebox-bounces+u.kleine-koenig=pengutronix.de@lists.infradead.org Subject: Re: [PATCH] net: fix checksum verification To: Sascha Hauer Cc: barebox@lists.infradead.org On Fri, Aug 09, 2013 at 09:32:37AM +0200, Sascha Hauer wrote: > On Fri, Aug 09, 2013 at 07:01:24AM +0300, Baruch Siach wrote: > > Checksum verification on data including its own checksum (as is the cas= e with > > IP headers) should give zero. Current code works well for the correct c= hecksum > > case, but fails to identify (most) errors. > > = > > Signed-off-by: Baruch Siach > > --- > > = > > Untested. From code inspection only. > > = > > net/net.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > = > > diff --git a/net/net.c b/net/net.c > > index 0bd9084..bd7a578 100644 > > --- a/net/net.c > > +++ b/net/net.c > > @@ -41,7 +41,7 @@ static unsigned int net_ip_id; > > = > > int net_checksum_ok(unsigned char *ptr, int len) > > { > > - return net_checksum(ptr, len) + 1; > > + return net_checksum(ptr, len) =3D=3D 0; > = > D'oh. There's a bug indeed. For a good packet net_checksum returns > 0xffff (all ones in an u16). So the check should be: > = > return net_checksum(ptr, len) =3D=3D 0xffff; with return net_checksum(ptr, len) + 1 net_checksum_ok returns always something >0 (i.e. success) because both summands are converted to unsigned, and so never catches an error[1], does it? > U-Boot has this instead: > = > return !((net_checksum(ptr, len) + 1) & 0xfffe); > = > From what I see both above should be equivalent so I wonder why U-Boot > has such a complicated code here. Some compiler optimization or is this > something I don't see? This isn't equivalent. The U-Boot code returns 1 iff net_checksum returns 0 or 0xffff; 0 otherwise. Best regards Uwe [1] well unless unsigned is only 16 bits wide which shouldn't be the case on all platforms barebox is running on. -- = Pengutronix e.K. | Uwe Kleine-K=F6nig | Industrial Linux Solutions | http://www.pengutronix.de/ | _______________________________________________ barebox mailing list barebox@lists.infradead.org http://lists.infradead.org/mailman/listinfo/barebox